Current internal combustion engines such as automotive internal combustion engines typically comprise an exhaust gas recirculating device (which is referred to as EGR device hereinafter) that recirculates a part of exhaust gas (which is referred to as exhaust gas recirculating gas or EGR gas hereinafter) to the intake system thereof for the purposes of improving fuel economy and reducing the NOx contents in the exhaust gas.
For such EGR devices, proposals have been made to prevent the clogging of an introduction port for introducing EGR gas into an intake passage. According to a proposal disclosed in Patent Document 1 (Japanese patent laid open publication No. 2008-75522), a distribution passage for EGR gas and blow-by gas is formed in a plate member provided between an intake manifold and a cylinder head in such a manner that a distribution passage outlet for blow-by gas (blow-by gas introduction port) is located downstream of a distribution passage outlet for EGR gas (EGR gas introduction port) with respect to the intake flow. Thereby, the structure around the intake passage of the engine can be simplified while the clogging of the distribution passage outlet for EGR gas with carbonized oil contents or the like that may be mixed in the blow-by gas can be avoided.
In a four-stroke engine, when an intake valve and an exhaust valve are simultaneously opened in an early part of an intake stroke (valve overlap), or when an intake valve is not fully closed in an early part of a compression stroke, a backflow of intake flow from the cylinder head to the intake manifold can occur. However, according to the proposal disclosed in Patent Document 1, because the distribution passage outlet for EGR gas is provided adjacent to the main part of the intake flow, when such a backflow occurs, carbon particles and oil contained in the blow-by gas may be deposited on an area surrounding the distribution passage outlet for EGR gas, and this could cause a clogging of the distribution passage outlet for EGR gas.